<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>判断时间段</title>
    <script>
        var time = prompt('您输入的数字是(0~23之间)')

        if (time >= 6 && time <= 12) {
            alert('上午好')
        } else if (time >= 13 && time <= 18) {
            alert('下午好')
        } else if (time >= 19 && time <= 23) {
            alert('晚上好')
        } else {
            alert('这是休息时间，不要说话！')
        }
    </script>
</head>

<body>

</body>

</html>